CA1125013A - Manufacture of cementitious products - Google Patents

Abstract

ABSTRACT

A rotating kiln or cooler for use in the manufacture of cementitious materials comprises a tubular body (1) mounted for rotation about the longitudinal axis thereof, a material being fed into the body at one end and removed at the other end. Air or combustion gases flow through the body (1) in the opposite direction to the material.
In order to improve heat transfer between the material and the air or gases, at least one ring (12) of lifting members (34) is provided on the interior periph-ery of the body (1). The members (34) lift the material and allow it to drop back to the bottom of the kiln, thus increasing the surface area of the material in contact with the air or gases.

Description

~5~3 . CEM~'N~ITIOUS MATERIALS
. _ This in-~7ention is for improvements in or relating to the manufacture of cementitious materials and'~is particular~ ~ -ly concerned with providing an improved method and apparatus for use in the manufacture of cementitious materials.
In the,manufacture of cementitious materials it is known to provide a rotating kiln in wh'ich raw feed material ' is fed in at one end. The kiln is rotated and is inclined at an angle to the horizontal such that the raw feed is fed in at the upper end of the kiln a~d as the kiln rotates the raw feed has water evaporated therefrom (if the raw feed is wet) as a result of heat being applied to the lower end ~' of the kiln. The raw feed gradua].ly dries to a non-liquid state, carbon dioxide is driven off from what is then rela-tively solid material and then that material is rendered 1~ into a clinker in a zone of the furnace known as the burning zone, before being cooled.
Heat which is supplied to a kiln may either be by a burner using a fossil fuel such as for example, coal, oil or gas or t,he kiln may have heat supplied thereto by electricity.
- The present lilvention is applicable to any form of a ,rotating ki,ln ~or use in the manufacture of a cementitious material.
It will be appreciated that in order to form the cementitious material the raw feed has not only to have the moisture evaporated 'therefrom, but has to be heated to a .
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sufficiently hi~h temperature in order to calcine the material into a cementitious clinker. This cementitious clinker after cooling is subsequently ground to a powder in a mill and mi~ed with othex materials in order to form a cementitious product. The clinker is formed in the ' burning zone and it is necessary thereafter to cool that clinker for storage and subsequent transportation. ~t will be appreciated that the clinker possesses heat and if the clinker is allowed to leave the kiln with that heat,, some of that heat will be wasted.
An object of the present invention is to remove some of the heat from the clinker,as it is cooling and transfer it to the cooler air entering the kiln.
It will also be appreciated that at the`entry of the raw feed to the kiln hot ~ases are leaving the kiln to pass up a chimnev and it is an object of the present inven-tion to transfer some of the heat from such hot gases to the raw feed as it enters the kiln.
Accordir.gly, the present invention provides a method o~ manufacturing a cementitious material in a rotating cement maki~g kiln having gases passing therethrough which comprises rotating the kiln, providing at least one riny of lifting members for the material around the internal periphery of the kiln to lift the material from the bottom of the kiln and allowing the material tc fall out of the lifting members to the bottom of the kiln.
In order to assist the transfer of heat ~etween the gases within the kiln and the material which commences as the raw feed and exits the kiln as a cementitious clinker the invention provides for the lifting of the material from the bottom of the kiln along which it progresses.
It will be appreciated that the material lies mainly on the bottom of the kiln and is lifted partly to one side as the kiln rotates. After a few degrees of rotation from the bottom the material falls back again to the bottom.

~2S~L3 It is desired therefore to lift the material further up the side of the kiln and over the top dead centre of the kiln in order to expose a greater surface of said material to the gases and thus to effect a better exchange of heat bet~een the -two. Such exchange of heat is from gases -to raw feed at one end of the kiln and from hot clinker to cooler air at the other or lower end of the kiln, i.e. where the clinker leaves the kiln.
The term kiln as used herein includes not only a kiln in which the cementitious clinker i.s made but inclu-des for the purposes of this specification a rotating member intG which hot cementitious clinker may be fed for cooling thexeof, such member will ke rotatable about a substantially horizontal axis and cool a.ir will enter such member and after exchange with the heated clinker the air passes into the kiln in which the ra~ feed is calcined to cementitious clinker~
Accordingly the present invention provides a rotating kiln for the man~fac~ure of cementitious material said kiln comprisins an elongate tubular member mounted for rotation about an a~i.s inclined to the horizontal, means for feeding matex.ial i-nto the kiln and means for permit-ting the exit of material from adjacent to the lower end of the kiln characterised in the provisi.on of at least ~5 one ring of li~ting members on the interior periphery of the kiln, said mer~lbers having the means to lift the mater-ial from adjacent the bottom of the kiln and allow the material to drop back to the bottom of the kiln.
The lifting members have an inlet opening through which the material enters and an exit opening from which the materia]. leaves and a passageway between the two open-ings so that as the kiln rotates, material held in the passageway between the two openings will subsequently fall from the said exit opening down to the bottom of the kiln again. The lifting members may comprise a series of tubes secured to the internal periphery of the kiln or they may ' be formed of refractory material by building blocks of desired material or of refractory material cast in situ within the ]ciln. The exit opening will desirably be of larger size than the inlet opening The lifting members will be in the form of a ring on the internal periphery of the kiln and a plurality of rings may be provided, each ring being separated by a banker ring or other means which restricts the flow of the material from one ring to the next, thus ensuring that the material is retained longer within the lifting members and thus lifted higher. The lifting members may if desired have a passageway extending radially inwardly so that th~
ma~erial ma~ fall out of the lifting members apart from -15 out of the axit o~ening of the members. The passageway through the lifting members from one opening to the other may either be para]lel to the axis of rotation of the kiln or may be inclined thereto. Said angle of inclination may either be in the direction of rotation of the kiln in which event it will assist the material to pass more rapidly through the lifting member, or may be in the oppos-ite direction to that of rotation of the kiln in which case it will reduce the speed at which the material passes through the lifting member.
~y effecting a transfer of heat between the raw feed or cementitious clinker on the one hand and the gases in the kiln, it is thought that for the same amount of heat ~ed to the kiln-a greater amount of cementitious clinker will be pr~duced or alternatively less heat will be needed by the kiln to produce the same quantity of cementitious clinker.
Reference is made to the drawings, in which:
Figure 1 is an elevation of a wet-feed cement kiln;
Figure 2 is a diagrammatic representation of a dry-feed cement kiln;
Figure 3 is a diagrammatic representation of a cement kiln having a cooler;

Figure ~ is ~ longitudinal cross-section of ~ portion of a cement kiln h.aving cne form of lifting members;
Figure 5 is a section on the line x~x in Figure 4, divided into four parts showing alternative constructions;
Figure 6 is a longitudinal cross-section of a portion of a cement kiln having an alternative form of lifting members;
lo Figure 7 i5 a section on line y-y in Figure 6; and Figures 8 to 16 are cross-sections corresponding to Figures 10, 11, 13, 1~ and 15 ~ein~ divided into three parts and Figure 16 into two parts, each part in any one Figure showing alternative configurations fox lifting members of the same general shape.
Referring first to Figure 1, a cement kiln comprises an elongate tubular steel body 1 supported on roller 2 at a small inclination to the, horizontal. The body 1 is 20 rotated by means of an electric motor 3 turning a pinion ~
in engagement with a ring gear 5. The body 1 is lined with refractory bricks, which are not shown in detail. A burner pipe 6 extends into the body 1 from the lower end thereo~
and is supplied with air from a blower 7 and pulverised 25 coal through a coal feed pipe.8.
The pulverised coal blown ~'nto the body ] burns as a jet which strikes the brick lining of the body 1 ~or rather, in use, the materials forming the cement clinke~ on the lining) raising the temperature to a level sufficient 30 for the cement clinker forming reaction to occur.
The cement-form.ing materials are introduced in the ~orm of an aqueous slurry into the body 1 of the kiln at the upper end thereof, as indicated by arrow S. The materials pass down the kiln through a conventional chain 35 section 9, in which the slurry is dried and ~roken into a powder, and which forms part of pre-heating zone ~, to a ~ 6 -C2 zone B 7 in which carbon dioxide is driven off, and thence to a ~urning zone C, in which the temperature is sufficient to enable the cement clinker fonming reaction to take place. The powdered materials fuse during the reaction and on moving down past the burning zone C into a cooling zone D form a cement clin~er. The clinker leaves the body 1 through apertures 10, passing through heat exch~r.~es 11 in which Eleat may be transferred to the combustion aix enteriny the kiln, improving combustion efficiency.
Rings 12 of the lifting members which may, for example, have lhe form illustrated in any of Figures 4 to 16, as hereinafter described, are mounted within the kiln body 1 at a location just upstream or the apertures 10l just upstream of the burning zone C and at I:he u~per end of the body lo The lowermost rings 12d serve to transfer heat from the hot clinker to the combustion air passing up the body 1 towards the flame. The m~ddle rings 12b transfer heat to the material from the hot gases from the burning zone, raising the temperature of the material more rapidly to that at which the carbon dioxide is driven off. The uppermost rings 12a transEer heat at a lower temperature from the gases leaving the kiln body in the direction of arrow G to the slurry entering the kiln body 1.
The dry-feed kiln illustrated in Figure 2 does not require the long pre-heating drying zone used in wet-feed kilns. The combined pre~heating and Co2 ~one s has a series of rings 12b of lifting members in which the material is raised towards the burning temperature, and rings 12d adjacent to the clinker outlet of the kiln to cool the clinker and pre-heat the combustion airO
The kiln body 1 of Figure 3 may be of either the wet-feed or dry-feed type. The pre-cooled clinker leaving the lowermost r~ngs 12d of lifting members passes into an external cooler 30 in which a series o~ rings 31 of lifting members is arranged. The cooler 30 rotates in a similar l3 - 7 ~
manner to the kiln~ and air is p~ssed thrcugh the cooler in the direction of arrow T~ some of the air being drawn t'hrough the'blower supplying air to the burner pipe 6 Very eficient heat transfer from`the 'clinker to the air 5 is obtained; the'clinker leaving the'cooler 30 can be sufficiently cool to handle manually.
Whilst the kilns descri~ed with reference to Figures 1, 2 and 3 are shown with'coal or gas fired burner's the invention is equally applicable to kilns having other forms 10 of heating, for example eIectricity.
Figures 4 and 5 illustrate forms of lifting members which may be constructed in refractory ~rick or ceramic materials and thus be suitable for use il~ or near the high ' temperature burning zone C of the kiln. Figure 5 is a 15 view up the kiln toward the inlet for the materials.
The steel shell 40 of the kiln has a lining of refractory bricks 41 except where the rings of lifting members are provided. The lifting members are f'ormed as - refractory blocks 42 mounted around the inner surface of 20 the shell 40. The blocks 42 have an inlet opening 43a through which the material passes t'o enter a passageway 43 leading to an exit opening 43b through which the material leaves the block 42. The surface of the passageways 43 are generally parallel to the surface o~ the shell 40 at their nearest 25 points to the shell 40, but slope inwardly towards the axis of the kiln at their nearest points to the axis. Thus the inlet openings 43a are smaller than the e~it openings 43b.
Adjacent rings of blocks 42 are separated from each other by banker rings 44 formed of refractory bricks which are 30 tapered on the surface facing inwardly of the kiln. These banker rings serve to reduce further the si~e of the inlet openings 43a thereby holding back the material in its pas-sage down the kiln and allowing time for the ro~ation of the kiln to lift the material up the side o the kiln. The 35 sectors 5A, 5~, SC and 5D show alternative arrangements of refractory ~lock 42 which can make up the rings of lifting members. Sector 5D shows the passageway 43 having a " ~ .

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tapered tubular lining member 45 ~hich ma~ serye to reduce abracion of the blocks b~ material passing through the passageway 43. The lining mem~ers 45 will be formed of a refractory material, which may ~e a ceramic or a metal, where the rings are located at a rnigh temperature zone of the kiln.
In use, the material will flow down the kiln in the direction of arrow M in Figure 4. Th~ lifting members serve several main functions. Firstly, the material tends to bank up on the upstream side of each ring and this causes the material to ride higher up the side of the kiln as the kiln rotates, thus presenting a larger surface area to the gases flowing up the 3ciln. Secondly, some of the material is carried around the kiln^, as it rotates, by the passageways 43. Thirdly, some of the material carried by the passageways 43 tend to fall out as the blocks pass over the top of their rotation path, the inward taper of the passageway 43 assisting this falling out, the resultant fall of material, which may form a 'curtain' across the kiln, greatly increasing the surface area of material in contact with the gases.
Fourthly, as the material passes through the passageway 43 in the blocks, heat is transferred between the blocks and the material, and as the blocks travel around the remainder of their circular path they are again heated or cooled by the gases flowing in the kiln. The direction ~o heat transfer will depend upon the locat-on of the rings; upstream of the burning zone heat is transferred from the gases to the material via the blocks, and down-stream heat is transferred from the material to the air.
The banker rings 44 delay passage of the materialdown the kiln through the rings and thus serve to increase contact time of the material with the rings and thus heat transfer. In some constructions the banker rings may be omitted.
The li~ting members shown in Figures ~ and 7 are : "~''' _. .. . ... . ~ .~!
~5~D~3 intended prim~ril~ for use at *he uppe~mo$t end of a wet-feed kiln, th~ ~embers comprising tapered tuhular steel ~odies 60 mounted on the lining bricks 61 of the shell 40 of the kiln by means of brackets 62 passing through or 5 between the bricks 61 and welded to the inne~ surface of the shell 40. The bodies 60 are partially closed at each end by steel grilles 63, and contain steel ~alls 64, or similar pieces of metal, which serve to scour the insides of the bodies 60, preventing blockage by the slurry ~
10 passing through in addition to further im~roving heat transfer Banker rings 44, as described with reference to Figures 4 and 5, separate the rings of ~odies 60.
Figures 8 to 11 show alternative shapes of passageways through the rinys of lifting members, similar to those 15 shown in Figures 4 and 5. In figures ~ and 9, tapered passageways are shown as before, whilst in Figures 10 and 11, untapered passageways are shown. Sec~ors lOA and llA show passageways whose axes are parallel to that of the kiln, whilst Sectors lOB and llB show passageways 20 whose axes are inclined to the direction of rotation of the kiln so as to slow the passage of material through the lifting members. ~rhe inclination referred to is clearly illustrated in the Figures. The passaaeways shown in Sectors lOC and llC are inclined in ~he opposite direction 25 of the passageways of Sectors lOB and llB so as to accelerate the flow of material through the lifting member. These alternative configurations enable ~ontrol to be exercised locally of the flow rate and hence heat transfer. Combin-ations of such different rings may be used.
Figures 12 to 16 show various forms of an alternative arrangement of li~ting members having passageways 120 through the blocks 121 forming ~he ring, the passageways 120 also opening radially inwardly of the kiln. This arrangement e~sures that a greater proportion or all o the material 35 carried up in the passayeways falls out as the passageways pass over the top of their path. Figure 12 shows passageways having an inner surface 122 which is inwardly tapered in the ~2~ 3 same manner as the inner surface o~ ~he passa~eways in, for example~ ihe em~odJment of Figure 8~ to assist the material in falling out. F~gure 13 ~hbws three sets of passageways similar to th~t of Figure 12, but without the 5 inward taper. In ~ector A of Figure 13 the passageways pass straight through the ring, whilst in Sectors B and C
the passageways are inclined relative to the direction of rotation of the kiln so as to slow passage of the material, in the case of 13B, or accelerate, in the case of 13C.
Figures 14 and 15 are generally similar to Figure 13, showing alternative shapes of passageways, whilst Figure 16 shows passageway~ which are twisted, rather than simply inclined to the kiln axis, the type shown in Sector B
tending to s;ow the material, whilst that in Se~tor C tends to 15 accelerate its passage down the kiln.
All rings of Figures 8 to 16 are shown from a position looking up the kiln towards the end at which the materials are introduced into the kiln. The rings may be formed ~rom blocks Gf any suitable shape, as shown in Figure 5.
A kiln having lifting members as described will, by virtue of thQ more efficient heat transfer to and from the material passing through it, the siIltering process depend-ing less on radiant heat from the lining, wasteless heat by radiation from the kiln and in the gases and clinker 25 leaving the kiln. Thus the throughput may be increased for a given energy consumption, or the energy consumption may be reduced for a given throughput of material.
A new kiln in accordance with the invention may be built shorter than conventional kilns of the same 30 capacity, with consequent savings in capital expenditure.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A rotating kiln for the manufacture of cementi-tious material, said kiln comprising in combination:
(a) an elongated tubular member mounted for rotation about an axis inclined to the horizontal and having a lower end, -the central cross-section of said tubular member being free from any fixed obstruction to the flow of gases through said tubular member;
(b) means for feeding a material in-to said tubular member;
(c) means for permitting the exit of material from adja-cent to the lower end of said tubular member;
(d) at least one lifting device, each said lifting device including:
i. at least one ring, each said ring including a plurality of lifting members rigidly fixed to the interior pe-riphery of said tubular member and extending radially inwardly of said tubular member for lifting material from adjacent to the bottom of said tubular member and for allowing the material to drop back to the bottom of said tubular member, each said lifting member includ-ing an inlet opening through which the material enters said lifting member, an outlet opening from which the material leaves said lifting member and a passageway for the material between said inlet and outlet openings;
and ii. banker rings disposed intermediate said rings for delaying passage of the material through said passage-way of said lifting members in said rings said banker rings including means for restricting said outlet open-ings of said lifting members.

2. The kiln as set forth in claim 1 wherein said banker rings include means for encouraging flow of material into said inlet openings in said lifting members of the next downstream one of said rings.

3. The kiln as set forth in claim 1 wherein said banker rings extend radially inwardly of the inner surface of said tubular member.

4. The kiln as set forth in claim 1 wherein said banker rings extend radially inwardly of the inner surface of said tubular member intermediate adjacent ones of said rings.

5. The kiln as set forth in claim 1 including at least two of said lifting devices located mutually adjacent one another and means for restricting said inlet openings through which the material enters said lifting members.

6. The kiln as set forth in claim 5 wherein said passageway of each said lifting member includes a radially inwardly directed further passageway from which the material may leave said lifting member.

7. The kiln as set forth in any of claims 1, 5 or 6 wherein each said ring of lifting members comprises a plurality of blocks refractory material, said blocks being contoured to provide said inlet opening, said outlet opening and said passageway.

8. The kiln as set forth in claim 1 wherein said tubular member includes a preheating zone, a burning zone and a cooling zone and wherein at least one of said rings of lifting members is disposed within said cooling zone.

9. The kiln as set forth in claim 8 wherein at least one of said rings of lifting members is disposed in proximity to said cooling zone.

10. The kiln as set forth in claim 9 wherein at least one of said rings of lifting members is disposed in proximity to said burning zone.